BIRC3 (Encoding cIAP2) Variants Result in Dysregulated RIPK1 Signaling Leading to Increased Epithelial Cell Death and...

Tumor necrosis factor (TNF) is a key driver of intestinal epithelial inflammation. The baculoviral inhibitor of apoptosis protein repeat-containing 3 (BIRC3) gene encodes the cellular inhibitor of apoptosis protein 2 (cIAP2), a known regulator of TNF signaling. Although genetic variants in components of the TNF signaling pathway have been reported, no human BIRC3 variants have been previously identified.

We screened exomes obtained from Crohn's disease (CD) patients from multiple centers for BIRC3 variants. We used cellular, mouse organoids, induced pluripotent stem cells-derived intestinal organoids, knock-in and knockout mouse models, and knockout zebrafish, as well as transcriptome analysis of various samples to determine pathogenicity of BIRC3 variants.

Rare and damaging BIRC3 variants were identified in 14 patients from 10 unrelated families with CD diagnosed between infancy and adulthood. Functional studies showed that BIRC3 deficiency caused impaired receptor-interacting protein kinase 1 (RIPK1) ubiquitylation, leading to RIPK1 autophosphorylation resulting in increased epithelial cell death. The p.H312Y cIAP2 variant identified in both our index and in another independent patient was mislocalizaed, and a knock-in mouse model of this BIRC3 variant (cIAP2^H312Y/+) had exacerbation of chemically induced colitis, whereas ciap1^-/+ zebrafish developed spontaneous colitis. Transcriptome analysis of mice organoids and zebrafish showed that BIRC3 deficiency led to inappropriate sustained activation of TNF-responsiveness genes in the absence of stimuli. Small molecule pharmacologic inhibition of RIPK1 or caspases attenuated intestinal inflammation in BIRC3-deficient intestinal organoids and cIAP2^H312Y/+ mice.

We establish BIRC3 deficiency as a cause of monogenic CD in both pediatric- and adult-onset patients and identify RIPK1 as a therapeutic target.